On progressive removal of the pancreas, the liver serine dehydratase [EC 4. 2. 1. 13] activity decreased in parallel to about one-tenth of the normal level on total pancrea-tectomy. The enzyme activity in pancreatectomized rats was not increased in response to treatments such as fasting, force-feeding of amino acids and hydrocortisone administration, which all caused, more or less, enhancement of the enzyme activity in sham-operated rats. Thus a pancreatic hormonc(s) -seemed to be involved in control of liver serine dehydratase activity. Glucagon was demonstrated to participate in elevating the enzyme activity in pancreatectomized rats and hydrocortisone was shown to play a “permissive” role, potentiating the induction of serine dehydratase by glucagon.